The present invention relates to gas diffusion electrode assemblies comprising a gas diffusion electrode and bonded thereto a metallic terminal, metallic edging material, resinous edging material, or structure for connection and to processes for producing the electrode assemblies. More particularly, the invention relates to gas diffusion electrode assemblies which each has bonded thereto a metallic terminal, edging material, or structure for connection and which, when used as a gas diffusion electrode for the electrolysis of sodium chloride, can be easily attached to an electrode pan and attain easy collection of electrons. The invention further relates to processes for producing the electrode assemblies and a method for bonding a silver material to a collector sheet as a gas diffusion electrode constituent.
In the sodium chloride electrolysis industry, the leakage of an electrolytic solution or decomposition gas from the cathode part in the case of using a gas diffusion electrode as an oxygen cathode has conventionally been prevented by sandwiching the electrode together with a packing between electrolytic cell frames.
However, electrolytic cells for practical use employ as the cathode a large electrode plate having dimensions of 1.2 mxc3x972.4 m. Electrode plates having a size of 1 m2 or larger have been found to have problems, for example, that it is virtually difficult to obtain such a large electrode as a single electrode plate, that the gas diffusion electrodes are difficult to handle because they have low mechanical strength and are hence apt to be deformed by their own weight, and that it is difficult to sufficiently feed electricity to the gas diffusion electrodes only through the periphery thereof.
Investigations are being made on a technique for attaching, for example, two or more separate small electrode plates to an electrode pan. This technique comprises employing gas diffusion electrodes each having a collector sheet gauze extending beyond the periphery of the electrode, welding the projecting parts of the gauzes to an electrode pan with a laser, and sealing the peripheral parts of the gas diffusion electrodes by applying a sealing material to the welded parts of the gauzes.
However, the technique described above is impractical because there is no sealing material which stably performs its function over long in caustic soda having a high temperature and high concentration and, hence, long-term operation results in liquid leakage. The liquid leakage not only reduces electrolytic performance but is causative of a decrease in electrode life.
There has been a desire for means which eliminates the liquid leakage, i.e., a gas diffusion electrode which can be tenaciously bonded to an electrolytic cell feeder part and easily attached to an electrolytic cell and which facilitates collection of electrons and sealing.
The joint between a gas diffusion electrode and an electrolytic cell feeder part, especially that part of the gas diffusion electrode which has a low bonding strength, is apt to suffer liquid leakage in long-term operation in caustic soda having a high temperature and high concentration. There is hence a desire for a technique for bonding a silver sheet as an edging material to a gas diffusion electrode, in particular, a technique for more tenaciously bonding the silver sheet to the surface silver material of a collector sheet.
An object of the present invention is to provide a gas diffusion electrode assembly which has satisfactory electrode plate handleability, can be easily sealed, and are free from liquid leakage.
Another object of the invention is to provide a process for producing the electrode assembly.
A still other object of the invention is to provide a method for bonding a gas diffusion electrode constituent to a silver material to obtain a gas diffusion electrode which shows a stable electrode performance over a long period of time and has a long life.
Other objects and effects of the present invention will become more apparent from the following description.
The above-described objectives of the present invention have been achieved by providing the following gas diffusion electrode assemblies (1) to (8) and processes for producing a gas diffusion electrode assembly (9) to (16).
(1) A gas diffusion electrode assembly comprising:
a gas diffusion electrode; and
a metallic edging material bonded to a peripheral part of the electrode.
(2) The gas diffusion electrode assembly of item (1) above, wherein the metallic edging material comprises a metal selected from the group consisting of silver, silver alloys, gold, platinum and palladium or comprises nickel or a nickel-based alloy, coated with any of these metals.
(3) A gas diffusion electrode assembly comprising:
a gas diffusion electrode; and
a metallic terminal bonded to the electrode.
(4) The gas diffusion electrode assembly of item (3) above, wherein the metallic terminal comprises a metal selected from the group consisting of silver, silver alloys, gold, platinum and palladium or comprises nickel or a nickel-based alloy, coated with any of these metals.
(5) A gas diffusion electrode assembly comprising:
a gas diffusion electrode; and
a resinous edging material bonded to a peripheral part of the electrode.
(6) The gas diffusion electrode of item (5) above, wherein the resinous edging material comprises a fluororesin or poly(phenylene sulfide).
(7) A gas diffusion electrode assembly comprising:
a gas diffusion electrode; and
a structure for connection, which comprises a combination of a thin silver sheet and a reinforcing material comprising a tough metal as a base, the structure for connection being bonded to a peripheral part of the gas diffusion electrode.
(8) The gas diffusion electrode assembly of item (7) above, wherein the reinforcing material comprises a metal selected from the group consisting of nickel, stainless steel and copper.
(9) A process for producing a gas diffusion electrode assembly, which comprises:
bringing a metallic edging material into contact with a peripheral part of a gas diffusion electrode which comprises superposed gas diffusion electrode constituents comprising a reaction layer sheet, a gas feed layer sheet and a collector sheet and which contains a fluororesin; and
hot-pressing the assemblage at a temperature of from the melting point of the fluororesin to 400xc2x0 C. and at a pressing pressure of 5 kg/cm2 or higher to bond the edging material to the gas diffusion electrode.
(10) The process of item (9) above, wherein the metallic edging material comprises a metal selected from the group consisting of silver, silver alloys, gold, platinum and palladium or comprises nickel or a nickel-based alloy, coated with any of these metals.
(11) A process for producing a gas diffusion electrode assembly, which comprises:
superposing a metallic terminal on part of a gas diffusion electrode which comprises superposed gas diffusion electrode constituents comprising a reaction layer sheet, a gas feed layer sheet and a collector sheet and which contains a fluororesin; and
hot-pressing the assemblage at a temperature of from the melting point of the fluororesin to 400xc2x0 C. and at a pressing pressure of 5 kg/cm2 or higher.
(12) The process of item (11) above, wherein the metallic terminal comprises a metal selected from the group consisting of silver, silver alloys, gold, platinum and palladium or comprises nickel or a nickel-based alloy, coated with any of these metals.
(13) A process for producing a gas diffusion electrode assembly, which comprises:
bonding a silver material to a collector sheet;
prior to the bonding, applying fine silver particles to the bonding surface of at least one of the collector sheet and the silver material; and then
hot-pressing the silver material with respect to the collector sheet.
(14) The process of item (13) above, further comprises roughening the bonding surface of at least one of the collector sheet and the silver material.
(15) The process of item (13) above, wherein the hot-pressing is carried out at a temperature of from 200 to 400xc2x0 C. and a pressure of 5 kg/cm2 or higher.
(16) A process for producing a gas diffusion electrode assembly, which comprises:
superposing a resinous edging material onto a peripheral part of at least one of a reaction layer and a gas feed layer of a gas diffusion electrode; and
hot-pressing the assemblage at a temperature not lower than the melting point of the resin and at a pressing pressure of 10 kg/cm2 or higher.